The conventional Fourier transform methods were found to give an inadequately accurae and complete spectrum of the quantum oscillation frequencies for some materials with complicated Fermi surface such as IV-VI compounds in the distorted phase. Because of this problem, the early de Haas-van Alphen data of SnTe could not be interpreted properly. The ‘two window Fourier transform'technique was developed, and it solved this problem successfully in the Fermi surface measurements of Pb1-xSnxTe and SnTe. In this technique, the spectrum analysis are performed twice for each set of data by using two different windows, refered as ‘strong window' and ‘weak window' respectively, so as to increase the signal to noice ratio and to detect components with weaker strength and to resolve neighbouring components of similar strength. Hence higher detectability and resolvability and better accuracy can be achieved. The analysis results of the pseudo-SdH simulation signal, consisting of 10 components with different amplitude, show that the error in frequency of the spectrum is less than 1%.